The long-range goal of the proposed studies is to identify therapeutic strategies to slow the progression of cell injury in cholestatic liver disease. Cholestasis, the slowing of bile flow, accompanies viral, immunologic and toxic liver disease. A major form of liver cell death during cholestasis is apoptosis. Hepatocyte apoptosis in cholestatic disease is due, in part, to the retention of endogenous cytotoxic compounds normally excreted in bile. Among these retained hepatoxins are bile acids. Since bile acids induce apoptosis in hepatocytes, it is likely that they contribute to ongoing pathology in cholestatic hepatic disorders. The objective of these studies is to delineate the cellular mechanisms involved in bile acid induced hepatocyte apoptosis. The specific aims are targeted to determine the mechanisms involved in the anti-apoptotic effect of two compounds, cyclic AMP and hepatocyte growth factor. The studies are conducted in primary cultures of rat hepatocytes and will look at post-translational events controlled by the cytoprotective agents, particularly protein phosphorylation. They will examine the role of the lipid kinase, phosphoinositide-3 kinase, in the anti-apoptotic action of cAMP and HGF since previous studies have demonstrated that the survival effect of both agents is prevented when this kinase is inhibited. A second aim of these studies is to investigate how the substrata to which hepatocytes attach is capable of modulating the cell death response. Attachment to certain extracellular matrices, such as fibronectin or collagen, decreases the sensitivity of hepatocytes to bile acid induced apoptosis. This protection is correlated with the ability of the hepatocytes to spread on the matrix. Experiments will be conducted to determine if this spreading is necessary and sufficient for the protective effect and if so what are the cellular mechanisms that promotes both spreading and survival. Since the extracellular matrix composition of the liver is modified in cholestatic disease, elucidation of the mechanisms involved in matrix induced hepatocyte survival may have implications in the design of treatment protocols in chronic liver disease.